When working with a large score on a large monitor, I often find it difficult to scan my eyes vertically to work on the exact same measure at a new instrument. For example, if I’m writing something in the woodwinds and then want to add something at the same measure in the percussion at the bottom of the score, it is often difficult to scan perfectly vertically with my eyes, so I have to use my finger or look at the measure number in both places to make sure, taking extra time. It would be nice to have a subtle shading or highlight that encompasses the area currently selected (or where the caret current is if nothing else is selected) to have instant visual feedback about where you’re scanning your eyes vertically.
I think “Show Playhead When Stopped” might work for you? Not quite what you’re asking for (as it would be wherever you hit play) but it should give you a vertical guide.
This is under General Preferences.
I think you can change the colour of the caret (according to other threads).
And if you like the idea of the playhead as a guide, there is a command to move it to the start of the selection (without having to play anything).
option/alt + P moves playhead to selection